This application proposes to study the physical interrelationships between mouse alloantigens on the cell surfaces of thymus-derived lymphoid cells. Since some of these antigens define functionally distinct subpopulations of lymphocytes and might be related to specific receptors on the cell surfacce, their physical interrelationships could be of vast importance. Our preliminary investigations into the new Qa antigens indicate that there are physical associations between these antigens and H-2D on the peripheral T lymphocyte. We would like to extend these studies to other lymphocyte alloantigens including the Ly series, Ia, H-2K, TL, and Thy-1 by use of blocking studies, quantitative absorption tests, and immunofluorescent techniques.